Machining with the use of rotary tools is done by cutting elements of the tool which have small angles, with the cutting edge viewed from the top, at the extreme points of the cutting edge just inside and outside the cutting zone, between which the active portion of the cutting edge is confined. The active portion of the cutting edge is, in turn, composed of two portions, namely, the main and secondary portions, which are divided by the nose of the cutting edge. The main portion of the cutting edge has a considerable length and removes a maximum amount of stock. In rotary tools, the active portion of the cutting edge is 4 to 8 times longer than that of conventional flat form tools designed for the same stock removal. The great length of the active portion accounts for great cutting forces. With great cutting forces, even minor deviations from the true geometrical shape of the workpiece lead to considerable fluctuations of the cutting force, especially at a perpendicular to the axis of rotation of the tool. Thus the cutting force is applied to a plane in which the rigidity of the tool is minimal. The result is vibration of the machine tool--fixture--cutting tool--workpiece system. Vibration has an adverse effect on the surface finish and puts limitations on the feed. These factors, in turn, reduce the efficiency of machining.
There is known a method for machining bodies of revolution with the use of a rotary tool having a circular cutting edge. The axis of rotation of the tool is in a plane parallel with the base plane extending through the axis of the machine tool centers. The plane of the cutting edge extends at an angle to the axis of the machine tool centers. The nose of the cutting edge is in a plane extending through the axis of the machine tool centers at an angle to the base plane. The tool is fed from the nose of the cutting edge towards the axis of its rotation.
Machining with a rotary tool produces a succession of microridges on the surface of the workpiece, whose height is in direct proportion with the roughness of that surface. The lateral surface of a microridge in the direction of the feed is formed by the secondary portion of the cutting edge which extends from the nose of the cutting edge in the direction opposite to that of the feed. The lateral surface of a microridge on the side opposite to the direction of the feed is formed by the main portion of the cutting edge extending from the nose of the cutting edge in the direction of the feed. The complete profile of a microridge is formed during two revolutions of the workpiece by portions of the cutting edge on the opposite sides of its nose. The length of the secondary portion of the cutting edge, which extends from the cutting edge nose in the direction opposite to that of the feed, does not exceed 8 percent of the length of the main portion which extends from the cutting nose of the cutting edge in the direction of the feed.
A rotary tool has cutting elements with a cutting edge radius greater by one or two orders of magnitude than the radius of the cutting edge at the nose of a conventional flat form tool. As a result of machining with a rotary tool, the surface finish is by one order of magnitude better than in the case of using a conventional flat form tool under the same conditions.
Increasing the feed leads to a greater height of the microridges and a greater length of the secondary portion of the cutting edge. This, in turn, increases the friction force applied to the cutting edge in the direction opposite to that of its rotation and reduces the speed of rotation. The result is a greater frequency of the tool vibration and greater roughness of the machined surface.
The machining method under review is disadvantageous in that a microridge is formed by a single active portion of the cutting edge, composed of the main and secondary cutting edge portions. The cutting edge has no portion to cut off the microridge formed by the active portion and thus improve the surface finish. Surface finish cannot be improved by increasing the amount of feed. There are no machining methods which would employ an additional cutting edge portion to remove stock and form microridges, with the active portion of the cutting edge flattening the microridges. Thus there are no methods of machining with the use of rotary tools which would guarantee good surface finish with great amounts of feed.